Based on the “naturalness” criterion, upper bounds on all superparticle masses as functions of the top quark mass are derived. These bounds give an objective criterion to test (or disprove) the idea of low-energy supersymmetry, as implemented in supergravity models. These bounds strongly differentiate weakly interacting superparticles, like charginos or neutralinos, lighter than 100–200 GeV, from strongly interacting ones, like gluinos or squarks which can become heavier than 1 TeV.